Low-Frequency Converter-Driven Oscillations in Weak Grids: Explanation and Damping Improvement

Low-frequency oscillations have been reported in several weak-grids-connected voltage-source-converter(VSC) systems. Although efforts devoted to understanding the parametric and sensitivity impact of VSC controller gains, a general formulation oscillation mechanism is still missing. Using transfer function dynamic modelling approach, we find that outer loop active power control's bandwidth mainly determines frequency. The PLL introduces large phase lag around frequency weak grids which decreases damping. A simple but effective PI+Clegg integrator (CI) compensator proposed replace standard compensating PLL's delay increasing results are verified real time digital simulator.